a. Field of the Invention
The present invention relates to a method and apparatus for mapping the location of a point within a body. More specifically, the present invention relates to a method and apparatus for mapping the location of a node, such as a distal end electrode of a catheter, disposed within a body and located at a point, which is desired to be tracked, through reference to a plurality of reference nodes, such as a plurality of electrodes disposed within a reference catheter, and interpolation between the node and the plurality of reference nodes. Further, the present invention, upon mapping, will filter out any motion artifacts which may distort the location and/or movement of the node.
b. Background Art
It is well-known that an element, or node, of a medical device may be tracked within the body of a patient by measuring electrical signals passing through tissues, as well as other anatomic structures, in the body, through a navigational system (sometimes called a location mapping system). The location of the node may also be tracked by other means, such as magnetic and ultrasound tracking means. As an example, intersecting electromagnetic fields may be utilized to track the location of one or more elements, such as one or more catheter tips (or, more accurately, one or more electrodes disposed on a plurality of catheters), which may be placed at a point within a body. Further, the addition of a reference node at a known, fixed location may be employed to determine the location, in relation to the reference node and other parts of a patient's anatomy, of the node, or element, which corresponds to the location of a point within the body.
Systems for tracking medical elements within a body are disclosed in various U.S. patents. For example, U.S. Pat. No. 5,297,549, entitled “Endocardial Mapping System,” issued on 29 Mar. 1994 discloses a mapping system utilizing an array of electrodes placed in a heart. In this reference, the shape of the chamber, and the location of the electrodes, are determined via impedance plethysmography. Further, electrical measurements taken from the electrode array and referenced to a surface contacting electrode are used to generate a three-dimensional map of electrical activity. In another embodiment, a two-dimensional map of the electrical activity within the endocardial surface is computed.
Additionally, U.S. Pat. No. 5,311,866, entitled “Heart Mapping Catheter,” issued on 17 May 1994, discloses a mapping catheter assembly. In this reference, a lumen is provided to accept a catheter which includes a distal tip electrode assembly. In operation, an array of electrode sites are deformed into a spherical shape after the assembly is placed in a heart chamber. A reference electrode assembly is advanced into contact with the heart wall to provide calibration information for the array.
For another example, U.S. Pat. No. 5,553,611, entitled “Endocardial Measurement Method,” issued on 10 Sep. 1996, discloses a method for taking a collection of measurements from a set of measurement electrodes in an effort to determine the position of a catheter in a heart chamber.
Further, U.S. Pat. No. 5,662,108, entitled “Electrophysiology Mapping System,” issued on 2 Sep. 1997, discloses a mapping catheter positioned in a heart chamber, in which active electrode sites are activated to impose an electric field within the chamber. The blood volume and wall motion modulates the electric field, which is detected by passive electrode sites on the preferred catheter. In the reference, electrophysiology measurements, as well as geometry measurements, can be taken from the passive electrodes and used to display a map of intrinsic heart activity.
Additionally, U.S. Pat. No. 5,697,377 (and its progeny), entitled “Catheter Mapping System And Method,” issued on 16 Dec. 1997, discloses a system and method for catheter location mapping. Three substantially orthogonal alternating signals are applied through the patient, directed substantially toward the area of interest to be mapped. A catheter, equipped with at least a measuring electrode for cardiac procedures, is positioned at various locations either against the patient's heart wall, or within a coronary vein or artery. A voltage is sensed between the catheter tip and a reference electrode, preferably a surface electrode on the patient, which voltage signal has components corresponding to the three orthogonal applied current signals. U.S. Pat. No. 5,983,126, entitled “Catheter Location System And Method,” issued on 9 Nov. 1999, is a continuation of this reference.
Further, U.S. Pat. No. 6,049,622, entitled “Graphic Navigational Guides For Accurate Image Orientation And Navigation,” issued on 11 Apr. 2000, and discloses a method for the acquisition of image data having an attached spatial coordinate system. A navigational guide can then employ the coordinate system to indicate the orientation of the imaged object and the location of the viewer with respect to the imaged object.
Additionally, U.S. Pat. No. 6,240,307, entitled “Endocardial Mapping System” (and its progeny) issued on 29 May 2001, discloses a system for mapping the electrical activity of a heart. The system includes a set of electrodes spaced from the heart wall and a set of electrodes in contact with the heart wall. Voltage measurements from the electrodes are used to generate three-dimensional and two-dimensional maps of the electrical activity of the heart. U.S. Pat. Nos. 6,603,996; 6,647,617; 6,826,420 and 6,826,421 are divisionals of this reference. Further, U.S. Pat. Nos. 6,640,119; 6,728,562 and 6,990,370 are derivatives of this reference.
Finally, U.S. Pat. No. 6,556,695, entitled “Method For Producing High Resolution Real-Time Images, Of Structure And Function During Medical Procedures,” issued on 29 Apr. 2003, discloses the acquisition of the images of a heart with a high resolution medical imaging system used to construct a dynamic high resolution 4D model.
The contents of each of the above-cited references (including their progenies as named herein) are herein incorporated by reference in their entireties.
One difficulty in conventional location mapping systems and techniques concerns the real and imaginary movements that such tracking instruments routinely detect and, more specifically, the difficulty in discerning between the two types of movements. “Real movements” are actual, physical movements caused by the motion of a patient's body as a whole, or by parts of the body in relation to one another. For example, respiration causes expansion of the chest and consequent displacement of the organs contained within the chest cavity, including the heart. Additionally, “imaginary” movements may further add to the motion created by the physical movements described herein. For example, respiration may also alter the electrical impedance distribution of the body by the introduction of air into the chest cavity. The variations in the electrical field may result in readings that suggest additional motion by the node. For purposes of the present invention, these real and imaginary movements are collectively referred to as “motion artifacts.”
Interventional navigational systems are used to map points within the body. These systems use electromagnetic mapping algorithms in conjunction with an image or model of the anatomical environment in which the tracked node (i.e., the node whose location is to be tracked) operates. Such images are often derived from external imaging equipment currently known in the art, such as computed topography (“CT”) and magnetic resonance imaging (“MRI”) equipment.
Often, the result is a surface model that may be interpolated from points in three dimensions (“3D”) collected from an internal tracking node. However, because such surface models are often static, the motion artifacts described above may be confusing and distracting to an operator, may affect the accuracy of the tracking, and, consequently, may negatively impact treatment quality.
Because therapies and procedures using such tracking systems are often exceedingly delicate, such motion artifacts are undesirable. Thus, a system that reduces or minimizes such motion artifacts would enhance the quality of care provided. Consequently, it would be advantageous to be able to eliminate, or substantially eliminate, both real and imaginary movement in a navigational mapping system.